The present invention relates to an installation for manufacturing a wound rigid tubular pipe.
Rigid tubular pipes thus wound are intended to be unwound and straightened to be installed subsea by a laying ship with a view in particular to carrying hydrocarbons. This pipe-laying technique is known as the reeled pipe system.
In the field of oil prospecting, a distinction is made between flexible pipes and rigid pipes. Reference may be made to specifications API 17B and 17J by the American Petroleum Institute for the definition of flexible pipes and to specification API 17 A for the definition of rigid pipes; it is recalled that flexible pipes have a minimum bend radius to which they can be bent without damage (often known as MBR for minimum bending radius) that is relatively small (for example a few metres) by comparison with rigid pipes whose minimum radius of curvature without plastic deformation is relatively large (for example several tens of metres).
Furthermore, for a flexible pipe, the MBR corresponds to a limit before irreversible damage occurs whereas in the case of a rigid pipe, the minimum bending radius corresponds to the onset of plastic deformation which can be reversed by straightening.
Laying systems for rigid pipes are described in specification API 17 A and a distinction is drawn therein between two types of laying depending on whether the lengths of pipe are welded at sea (stove piping) or welded on land (reeled pipe).
The first type of laying itself has three main subdivisions, “S-lay”, “J-lay” and “G-lay”.
In the “S-lay” technique, the lengths of pipe are assembled horizontally on the deck of the ship to form the pipe and the pipe is made to follow, in a depth of water, an S-shaped path with a point of inflection and a very large radius of curvature so as to prevent it from experiencing plastic deformation. The pipe leaves the ship at an oblique angle with respect to the surface of the water, using an inclined stinger. This technique is suitable only for shallow and moderate laying depths, because otherwise the weight of the string of pipe already laid runs the risk of bending and plastically deforming the pipe where it leaves the stinger. This is why other techniques have had to be developed for greater depths of water.
In the “J-lay” technique, the lengths of pipe are assembled on an inclinable tower of the laying ship that is positioned close to vertical, the lengths thus being welded together in the direction in which the pipe is laid, thus avoiding any plastic deformation at this stage, the assembled pipe then being submerged, still without plastic deformation. The inclination of the tower is, in particular, dependent on the depth of water and it makes it possible to avoid the point of inflection that there is in the “S-lay” technique. Reference may be made to document U.S. Pat. No. 5,464,307 which illustrates this laying technique.
In the “G-lay” technique, illustrated in particular in document GB 2 287 518 A, lengths of pipe are assembled horizontally on the deck of a ship as in the case of the “S-lay” technique; the pipe formed is sent towards the bow of the ship then returned towards the stern by a large wheel giving rise to plastic deformation in the pipe, after which this pipe passes through straighteners and a succession of multi-track tensioners, then is launched into the water at a certain angle of inclination that can be chosen according to the depth of water to avoid plastically deforming the pipe at the submerged string. In an alternative form described in document GB 2 296 956 A, the pipe, already assembled in lengths on the deck, is sent to an arched gutter placed at the top of an inclinable ramp provided with tensioners or gripping jaws; the two inflections that the pipe undergoes lead to plastic deformation of the pipe and make the use of straigteners necessary. The laying speed using the “G-lay” technique is relatively slow.
The second type of technique for laying rigid pipes, in lengths welded on land, known as the reeled pipe system, is illustrated for example in document GB 2 025 566 A in which the pipe, welded in long lengths (in excess of 1 km for example) at the dockside, is then wound with plastic deformation around a vertical reel (which may reach as much as 15 to 20 metres in diameter) situated on the laying ship moored dockside.
The pipe is assembled on the dockside in an assembly base known as a spool base and the length of the lengths is dependent on the space available. The winding of the pipe consists in winding a first length then stopping winding to connect it to a second length by welding. This welding needs to be checked then covered with a coating to preserve it from corrosion in particular. These operations are lengthy and delay the loading of the laying boat still further.
After the laying ship has reached the laying site, the pipe is unwound again from the reel with plastic deformation and passed through a straightener-distributor guide before being taken up by the tracked conveyors of an inclinable laying ramp provided in a region for submerging the pipe at the stern of the ship and the inclination of which is chosen to suit the laying depth.
In order to reduce as far as possible the length of time for which the laying ships are occupied with operations other than actual laying, and in particular with operations of loading the rigid pipes, new rigid pipes are produced while the laying boat is submerging a pipe.
One problem that arises and that the invention described in document EP 0 909 254 B1 aims to solve is therefore that of manufacturing the entire pipe, or at the very least very long lengths of pipe, before the arrival of the laying boat.
To do this, the rigid pipe is wound on itself with a radius of curvature greater than 150 metres in order to avoid plastically deforming it, then it is unwound and wound onto a storage reel mounted on the laying boat moored dockside. In that way, the winding of the pipe onto its storage wheel can be performed continuously and the time spent connecting the lengths is eliminated.
Given the size of the laying boat storage reel, measuring of the order of about ten metres, the rigid pipe is plastically deformed during winding.
However, the unit for assembling and storing the rigid pipes (otherwise known as a spool base) is too large and in order to remedy this, the idea has been had for the rigid pipe to be wound up on the water, deforming it within its elastic limits so as not to plastically deform it. Thereafter, it is conveyed thus wound to the laying site.
These methods have been described in documents WO 00/11388 and U.S. Pat. No. 4,260,288.
The first document describes the production of a rigid pipe by assembling rigid tubes then forming a spiral on the surface of the water using floating guide means. The rigid pipe thus wound in a mean plane roughly parallel to the surface of the water forming a very large assembly about 250 metres in diameter, is then transported by two tugs to the laying boat. The latter is designed to guide the pipe to deposit it on the seabed, while the tugs pull it along and pay it out upstream.
The second document also discloses the formation of a rigid pipe which is wound on the water in a plane parallel to the surface of the water, at the dockside on floating winding means. These floating winding means are then towed out to the laying site then stood up vertically to pay the pipe out.
Given the size of the assemblies formed by these wound rigid pipes which are rendered necessary in order not to plastically deform the said pipes, otherwise they would have to be straightened on the laying vessel, their transportation is rather uneconomical. Indeed, it takes a great deal of power to drag the pipes thus wound through the water.
Still with a view to reducing the time for which the laying boat is unavailable for laying and to transporting the pipes produced on land to the laying site, but reducing significantly the size of the rigid pipes as wound according to the preceding document, document U.S. Pat. No. 4,117,692 has conceived of the idea of plastically deforming the pipe and of winding it onto a storage reel arranged horizontally on the surface of the water.
However, transporting the pipe by dragging through the water the storage reel which nonetheless exhibits a certain resistance to the water as it moves along, is also rather uneconomical.
In addition, in these methods where the rigid pipe is moved through the water, any debris floating on the surface is likely to damage it.
To overcome this, document EP 0 868 621 has conceived of the idea of winding the rigid pipe onto a storage reel mounted on a boat by plastically deforming it; the pipe then being transported to the laying boat then rewound onto a storage reel belonging to the laying boat so that it can then be reeled out to the bottom of the water.
However, it is found that transferring from one reel to the other on the high seas is rather awkward given the relative motion of the boats due to the swell. In addition, although this solution makes it possible to avoid unavailability of the laying boat, it does not, however, solve the need to have a land-based manufacturing base of the spool base type, with the aforementioned problems of space. The problems of unavailability time are then transferred to the supply boat which transports the rigid pipe out from the manufacturing base to the laying boat.